1. Field of the Invention
The present invention relates in general to an automotive air conditioner, and more particularly to an automotive air conditioning unit which comprises generally a casing defining therein an air passage with air inlet and outlet openings, an evaporator installed in an upstream portion of the air passage and a heater installed in a downstream portion of the air passage, an air intake unit connected to the air inlet opening of the air passage and an electric blower installed in the air intake unit for producing an air flow directed toward the air outlet opening through the air passage.
2. Description of Prior Art
In order to clarify the task of the present invention, two known automotive air conditioning units will be described with reference to FIGS. 21 and 22 of the accompanying drawings.
In FIG. 21, one known automotive air conditioning unit 3 is shown, which is constructed compact in size for providing front passengers with a larger foot space. The unit 3 generally comprises a casing 6, an evaporator 1 installed in a lower portion of an interior of the casing 6 and a heater 2 installed in a middle portion of the interior. Both the evaporator 1 and the heater 2 are inclined for a compact construction of the unit 3. The casing 6 is formed at a lower part of a side wall thereof with a generally rectangular air inlet opening 4 through which air from an air intake unit (not shown) is introduced into a triangular space provided below the evaporator 1. Between the evaporator 1 and the heater 2, there is arranged a pivot door 5 which controls the ratio between the amount of air directed toward an air mixing chamber AM through the heater 2 and the amount of air directed toward the air mixing chamber AMC bypassing the heater 2.
In FIG. 22, the other known automotive air conditioning unit 3xe2x80x2 is shown, which is similar to the above-mentioned unit 3. However, in the unit 3xe2x80x2 of this drawing, a slide door 7 is used in place of the above-mentioned pivot door 5. Due to the nature of the slide door 7, compactness of the unit 3xe2x80x2 is much assured as compared with that of the unit 3 of FIG. 21.
However, in the above-mentioned known units 3 and 3xe2x80x2, under operation, the triangular space defined below the evaporator 1 is subjected to uneven pressure distribution due to the inclined arrangement of the evaporator 1 and the rectangular shape of the air inlet opening 4. The uneven pressure distribution brings about uneven air flow throughout the air passing area of the evaporator 1 and thus lowers the performance of the same.
The reason of the uneven air flow through the evaporator 1 will be briefly described with reference to FIGS. 23 and 24.
FIG. 23 is a plan view of the lower portion of the unit 3 or 3xe2x80x2. That is, due to unbalanced air flow rate between larger and smaller areas of the triangular air inlet opening 4 and unbalanced air flow resistance in the triangular space between one side facing the larger area of the inlet opening 4 and the other side facing the smaller area of the same, there is produced an air swirl xe2x80x9cSxe2x80x9d at a central portion of the space which causes a pressure drop at such portion. Thus, smoothed air flow is not carried out at a central portion of the evaporator 1. Furthermore, as is seen from FIG. 23, the air flow passing through the larger part xe2x80x9cAxe2x80x9d of the air inlet opening 4 is subjected to a pressure increase each time it collides against walls xe2x80x9cBxe2x80x9d and xe2x80x9cCxe2x80x9d of the case 6, and finally, the pressure is much increased at the point xe2x80x9cDxe2x80x9d where it collides against the other air flow passing through the smaller part xe2x80x9cExe2x80x9d of the opening 4. FIG. 24 is a graph depicting the manner of the air flow through the evaporator 1 with respect to the positions xe2x80x9cAxe2x80x9d to xe2x80x9cExe2x80x9d. Pressurized areas are indicated by a shadow. As is seen from this graph, increased air flow appears around an area from the position xe2x80x9cBxe2x80x9d to the position xe2x80x9cCxe2x80x9d and around the position xe2x80x9cDxe2x80x9d and poor air flow appears at the other areas, which causes an uneven air flow through the evaporator 1 and thus lowers the performance of the same.
Usually, as is seen from FIG. 23, a drain pipe 9 is provided at a front wall of the casing 6, which communicates the triangular space of the casing 6 and the interior of the engine room. Thus, under operation of the air conditioner, water drops produced when moisture touches the cold outer surface of the evaporator 1 are led into the engine room. However, due to generation of the air swirl xe2x80x9cSxe2x80x9d in the space, the water:drops or water is not smoothly drained to the engine room through the drain pipe 9. In a worst case, the water drops or water is forced to flow backward toward the air intake unit under a certain running of an associated motor vehicle. This may bring about a trouble of the electric blower in the air intake unit.
It is therefore an object of the present invention to provide an automotive air conditioning unit which is free of the above-mentioned drawbacks.
A main object of the present invention is to provide an automotive air conditioning unit which can suppress the undesirable backflow of water drop or water toward the air inlet opening.
A second object of the present invention is to provide an automotive air conditioning unit which allows an even air flow throughout the air passing area of the evaporator even when the evaporator is inclined and the air inlet opening is generally triangular in shape.
According to a first aspect of the present invention, there is provided an air conditioning unit which comprises a casing having air inlet and outlet openings which are connected through an air flow passage defined in the casing, the casing including a bottom surface in the vicinity of the air inlet opening; an evaporator arranged in the air flow passage; a heater arranged in the air flow passage at a position downstream of the evaporator; an air flow control door for controlling a ratio between an air amount flowing in a heater-bypassing passage which extends from the evaporator to the air outlet opening bypassing the heater and an air amount flowing in a heater-passing passage which extends from the evaporator to the air outlet opening through the heater; a water guide groove provided at the bottom surface of the casing at a position opposite to the position where the air inlet opening is provided; a drain pipe held by the casing and connected to the water guide groove; and a plurality of water backflow obstruction projections formed on the bottom surface in an area defined between the water guide groove and the air inlet opening, each projection being shaped and oriented so as to obstruct a flow of water in a direction from the water guide groove toward the air inlet opening.
According to a second aspect of the present invention, there is provided an air conditioning unit which comprises a casing having air inlet and outlet openings which are connected through an air flow passage defined in the casing, the casing including a bottom surface in the vicinity of the air inlet opening, the air inlet opening being generally triangular in shape so that the height of one side of the air inlet opening is greater than that of the other side of the same; an evaporator inclined and arranged in the air flow passage; a heater inclined and arranged in the air flow passage at a position downstream of the evaporator; an air flow control door for controlling a rate between an air amount flowing in a heater-bypassing passage which extends from the evaporator to the air outlet opening bypassing the heater and an air amount flowing in a heater-passing passage which extends from the evaporator to the air outlet opening through the heater; a water guide groove provided at the bottom surface of the casing at a position opposite to the position where the air inlet opening is provided, the water guide groove having a slanted bottom; a drain pipe held by the casing and connected to a lower portion of the water guide groove; and a triangular projection formed on the bottom surface of the casing, the triangular projection being oriented so that one apex of the same is directed toward a rear wall of the casing and an opposite side of the apex faces toward a front wall of the casing, the rear and front walls being positioned near the one and the other sides of the air inlet opening respectively.